Multi-layer coaxial vaso-occlusive device

Abstract

A vaso-occlusive device includes inner, intermediate, and outer elements arranged coaxially. The inner element is a filamentous element, preferably a microcoil. The intermediate element is made of a non-metallic material, preferably an expansile polymer. The outer element is substantially non-expansile and defines at least one gap or opening through which the intermediate element is exposed. In a preferred embodiment, when the intermediate element is expanded, it protrudes through the at least one gap or opening in the outer element and assumes a configuration with an undulating, convexly-curved outer surface defining a chain of arcuate segments, each having a diameter significantly greater than the diameter of the outer element. The expanded configuration of the intermediate element minimizes friction when the device is deployed through a microcatheter, thereby reducing the likelihood of buckling while maintaining excellent flexibility. The result is a device with enhanced pushability and trackability when deployed through a microcatheter.

The invention claimed is: 
     
       1. A vaso-occlusive implant system insertable into a vascular malformation, comprising:
 a flexible elongate delivery apparatus having a proximal end and a distal end: 
 a vaso-occlusive implant removably coupled to the distal end of the flexible elongate delivery apparatus comprising:
 an elongate inner element formed from an expansile material that remains in an expanded state when located within a human body, and, 
 an outer element coaxially surrounding a length of the inner element, the outer element having a diameter substantially fixed from expansion and defining an open area between longitudinally-adjacent regions of the outer element that extends along a portion of the length of the inner element through which more than about 40% of a surface area of the inner element is exposed such that the expansile material is expandable through the open area and radially beyond the outer element. 
 
 
     
     
       2. The vaso-occlusive implant system of  claim 1 , wherein the inner element includes an expansile polymeric material. 
     
     
       3. The vaso-occlusive implant system of  claim 2 , wherein the expansile polymeric material comprises a hydrogel. 
     
     
       4. The vaso-occlusive implant system of  claim 3 , wherein the hydrogel is of a type that expands in response to a change in an environmental parameter. 
     
     
       5. The vaso-occlusive implant system of  claim 4 , wherein the environmental parameter is selected from the group consisting of temperature and pH. 
     
     
       6. The vaso-occlusive implant system of  claim 1 , wherein the outer element is formed of a helically-wound filament. 
     
     
       7. The vaso-occlusive implant system of  claim 1 , wherein the inner element comprises at least two concentric microcoils. 
     
     
       8. The vaso-occlusive implant system of  claim 1 , wherein the inner element defines a lumen containing a hollow, tubular core element. 
     
     
       9. The vaso-occlusive implant system of  claim 1 , wherein the inner element defines a lumen containing a substantially solid core element. 
     
     
       10. The vaso-occlusive implant system of  claim 1 , wherein at least one of the inner element and the outer element includes a material selected from the group consisting of at least one of a drug, a bioactive agent, a therapeutic compound, cellular material, genes, collagen, and protein. 
     
     
       11. A vaso-occlusive implant system comprising:
 a flexible elongate delivery apparatus having a distal end; 
 a vaso-occlusive implant releasably coupled to the distal end of the flexible elongate delivery apparatus, comprising:
 an expansile element having a surface area and remaining in an expanded state when in a physiological environment, 
 an outer element having a substantially non-expandable diameter and coaxially surrounding a length of the expansile element, 
 an open area formed between longitudinally-adjacent portions of said outer element, said open area exposing a portion of the surface area of the expansile element along the length of the expansile element, the outer element exposing more than about 40% of the surface area of the expansile element such that the expansile element is expandable through the open area and radially beyond the outer element. 
 
 
     
     
       12. The vaso-occlusive implant system of  claim 11 , wherein the expansile element includes an expansile polymeric material. 
     
     
       13. The vaso-occlusive implant system of  claim 11 , wherein the expansile element comprises a hydrogel. 
     
     
       14. The vaso-occlusive implant system of  claim 11 , wherein the outer element is a coil having spaces between each turn of the coil that defines the open area. 
     
     
       15. A vaso-occlusive implant system comprising:
 a vaso-occlusive implant releasably coupled to a distal end of a flexible elongate delivery apparatus, comprising: 
 an expansile element having a surface area and maintaining a volumetrically expanded state when inside a human body, 
 an outer element having a substantially non-expandable diameter and being coaxially coiled around the expansile element to define an open space between loops of the outer element that expose more than about 40% of the surface area of the expansile element such that the expansile element is expandable through the open space between the loops and radially beyond the outer element. 
 
     
     
       16. The vaso-occlusive implant system of  claim 15 , wherein the expansile element comprises a hydrogel. 
     
     
       17. The vaso-occlusive implant system of  claim 15 , wherein the expansile element is a hydrogel expands in response to a change in an environmental parameter. 
     
     
       18. The vaso-occlusive implant system of  claim 17 , wherein the environmental parameter is selected from the group consisting of temperature and pH.